1. Field of the Invention
This invention pertains to an unsupported decorative film of a polymeric composition having controlled permanent tack for temporary adhesion to all types of surfaces and a method of making said film. The film may be used for decorative purposes, may or may not be transparent to light and may be colored. The decorative formed film of this invention is of value in the field of arts and crafts.
2. Description of the Prior Art
The principal object of this invention is to provide a decorative film as an arts and crafts medium which is tough, flexible and permanently tacky. The film is designed to be arranged in a decorative, physical form and to be itself decorative. In order to be able to display this decorative formed film and to change the display from time to time, it is necessary that this decorative formed film be able to stick to many types of surfaces and have a permanent tack. The person using this art form can make a decorative art creation in the form of a film which may or may not be transparent to light, yet can bear color, much like tinted glass. To achieve this principal object, the film must be tough, flexible and adhesive. The most important property of this decorative formed film is that it have the proper permanent tack which will allow the formed film piece to be placed upon any surface, this placement supporting the decorative film piece, and which will allow the removal of the decorative film piece from one surface and its replacement on another surface without any loss of tack.
Thus, the polymeric composition of this invention must possess some very unique properties. In a search of the literature and of the marketplace, the inventors found that each apparently suitable polymer had one or more shortcomings. The inventors were searching for a film forming polymeric composition with the appropriate controlled permanent tack. The tack level has to be of such a nature as to stick to many different kinds of surfaces over a broad temperature range.
A permanently tacky adhesive or compound is not new or novel. There are many such compositions in use. However, these formulations were designed mainly as adhesives to stick one object to another object on a temporary basis, such as the adhesive on a finger bandage. But these adhesive masses would not be acceptable to support or make the decorative formed films of this invention.
Tack is a very difficult property to define. It certainly implies stick, as for example, the human skin must have a degree of tack to objects, or our hand would not be able to pick up or hold things rather easily. It is not only a chemical property as defined by molecular weight, solubility, or incompatibility of substances, but is also a mechanical property, as defined by displacement, deformation and contact. So, it is known that both chemical and mechanical considerations would have to be employed. It is also known that simple physical testing was not sufficient, for tack is too complex a property to evaluate with one simple test, but rather it would require painstakingly long empirical studies of trial and error and of end use evaluation on all kinds of surfaces, under all kinds of conditions of heat, moisture, and temperature.
It is common knowledge that tack, or permanent tack, can be achieved by the 60-40 principle. This says that 60 parts of a high molecular resin mixed with 40 parts of a low molecular resin or compound will result in a tacky mass. This principle holds quite well. However, compositions of this design were not acceptable to the requirements of this invention. They suffered from draw backs of cold flow, creep, migration, extreme variability of tack as to temperature, and complete loss of tack on exposure to moisture. Long term aging became a problem, the degree of tack would gradually lessen, and a lot of the composition in time would lose their tack.
To have a clear film that is transparent, the polymeric composition must be amorphous. This requirement eliminates a lot of polymers. However, amorphous or noncrystalline structures are more prone to permanent change when exposed to forces of chemical or mechanical stress. Hence, the amorphous polymer used in this invention must be very stable chemically, and not too thermoplastic so as to hold an acceptable level of physico-mechanical stability, especially as it relates to tack.